The present invention relates to an electric lamp which includes an end-of-life device that will safely extinguish the source of light when an outer lamp envelope is broken, without adversely substantially affecting lamp efficacy or providing an undesirable second light source during normal lamp operation. The present invention is particularly of interest regarding a tungsten halogen lamp.
A problem with some electrical lamps is that they present a fire hazard and may cause burns should the outer lamp envelope break. Although there is more than one type of lamp with respect to which this problem applies,the problem is particularly applicable to tungsten halogen lamps. Due to higher efficacy and coil temperatures, tungsten halogen lamps are attractive as replacements for ordinary incandescent filament lamps for general service lighting. However, tungsten halogen lamps typically operate at high bulb wall temperature and high internal pressure. For these reasons, tungsten halogen lamps are usually operated in fixtures with shielding to protect against accidental contact. The use of special fixtures increases the cost of using a tungsten halogen lamp and limits its usefulness to those applications where use of such a fixture is practical. In an alternative embodiment, it is known to seal the typical halogen capsule in an outer envelope having a thick wall that performs the shielding function. However, the use of thick walls increases the cost of the lamp and reduces the transmission of light. In addition, the thick walls of the lamp adds to its weight which can be a problem with some fixtures.
The use of a tungsten halogen lamp having a thin outer envelope is well known. However, such lamps present a potential safety hazard should the outer envelope break and the inner halogen capsule continue to operate. In particular, the wall temperature of the tungsten halogen inner capsule is high enough to cause bums and to ignite various materials such as paper and fabric. The safety problem is compounded due to the fact that such lamps are intended as replacement lamps for general service incandescent lamps and therefore are likely to be used in a wide variety of lighting fixtures, some of which could easily be tipped over or damaged in such a way as to break the outer glass envelope exposing the still burning inner halogen capsule.
The use of other types of lamps involve problems similar to those of tungsten halogen lamps. For example, high pressure discharge lamps include an inner arc tube contained within an outer envelope. One of the functions of the outer envelope is to permit passage of visible light, and block ultraviolet radiation, emitted by the inner arc tube during use of the lamp. Should the outer envelope be broken, such ultraviolet radiation will be emitted out of the lamp into the environment proximate the lamp.
A number of ways have been disclosed to interrupt electrical current to an inner lamp in the event of damage to an outer lamp envelope. One example known for use with a high intensity discharge lamp involves positioning an oxidizable fuse within the outer envelope of the lamp and in series with the lamp circuit. Such fuse oxidizes and interrupts the lamp circuit in the event the outer envelope breaks and exposes the fuse to air, thereby extinguishing the lamp. One of the concerns in manufacturing such lamps is providing a satisfactory manner in which to support the lamp capsule and fuse element within the outer envelope. It is known to fabricate such lamps by electrically and mechanically connecting the fuse directly to electrical conductors within the outer envelope by welding and the like. This may involve a complicated fabrication procedure, and in some instances it may be difficult to accurately control the length of the fuse. In addition, such lamps may include fairly complicated supports for the lamp capsule contained within the outer envelope. Such supports typically include straps which surround the capsule at opposite ends thereof and are attached to one or more support rods extending from an inlead protruding from the lamp stem. An example of such a high intensity discharge lamp which includes an oxidizable link within the outer envelope is described in U.S. Pat. No. 4,361,782. In this patent. the inner lamp capsule is supported within an outer lamp envelope by strap clips welded to a rod which is welded to an inlead extending from the lamp stem the rod extending to a looped clip which engages an anchoring dimple of the outer envelope. The oxidizable link provides part of the lamp circuit by being connected directly to an inlead and a main electrode.
In another known high intensity discharge lamp, described in U.S. Pat. No. 4,305,020, a current-interrupting device is electrically and mechanically connected between the inner capsule lead wire and the capsule supporting frame. Such an embodiment requires a similarly complicated fabrication procedure, adding to the cost of the lamp.
It is an object of the present invention to provide an improved support for a lamp capsule and an end-of-life device positioned within an outer envelope.
It is another object of the present invention to obviate the disadvantages of the prior art by providing an improved support for a lamp capsule and an end-of-life device positioned within an outer envelope.
A further object of the present invention is to provide an economical, efficient and high quality support for a lamp capsule and end-of-life device positioned within an outer envelope.
Another object of the present invention is to provide an electric lamp which includes the support of the present invention.
Yet a further object of the present invention is to provide a tungsten halogen lamp which includes the support of the present invention.
A further object of the present invention is to provide an improved method of coupling a lamp capsule and an end-of-life device to a lamp stem.
Another object of the present invention is to provide a less costly manner of supporting a lamp capsule and an end-of-life device in place within an outer lamp envelope.
Yet a further object of the present invention is to provide support for a lamp capsule and end-of-life device, within an outer lamp envelope, that simplifies manufacturing, reduces component count and ensures accurate control of fuse length.
Another object of the present invention is to provide a support for a lamp capsule to which an end-of-life device can be readily attached.
This invention achieves these and other objects by providing support, for use with an electric lamp having a sealed outer envelope enclosing an environment, a lamp capsule within the environment, a first lead wire and a second lead wire extending through the lamp capsule, a first electrical conductor a second electrical conductor extending through the outer envelope and being electrically connected to the first lead wire and the second lead wire, respectively. An end-of-life device is provided within the environment electrically connected in series with the first lead wire and the first electrical conductor. The support comprises a first portion mechanically connectable to the lamp capsule, a second portion electrically connectable to the first lead wire and to the end-of-life device, and a third portion electrically connectable to the first electrical conductor and to the end-of-life device. The support joins the first portion and the second portion, a section of the third portion being removable to separate, and form a gap between, the second portion and the third portion. A lamp including the support of the present invention, and a method of coupling a lamp capsule and end-of-use device to a lamp stem, are also provided.